Invasive Species of Concern in Maryland

ANNAPOLIS, MD (May 27, 2004) - Is it Shakespeare? No, it’s Sharka, a viral disease of plums and other stone fruits that has spread steadily from eastern to western Europe over the last 80 years. So far, the virus has not been found in Maryland. Officials and fruit growers want to keep it that way. The Maryland Invasive Species Council has chosen Sharka, also known as plum pox, as its May Invader of the Month because of the risk it poses to the Maryland’s orchard industry should it cross the state border from Pennsylvania, which has identified the disease in its stock.

To protect its industry, Maryland has conducted surveys of its commercial orchards and nurseries since 2000. Currently, surveys are underway in the northern counties of Maryland to test for the plum pox in backyard situations that are within one mile of commercial orchards. Selected commercial orchards and nurseries in these counties will also be surveyed to support the national survey program.

Sharka, also known as plum pox, is considered the most serious disease affecting stone fruit like peaches, apricots, nectarines, plums, and almonds. It is transmitted by several different aphid species, and by humans through grafting with infected budwood and transporting infected nursery stock but has no harmful affect on humans. Because of Sharka’s detrimental affect on the production of stone fruits, various countries have imposed tight quarantine restrictions to prevent the spread of infected nursery stock and budwood.

Plum pox virus causes different symptoms in different fruit trees. In peaches, infection ranges from almost no symptoms to yellowing bands and ring patterns on young leaves, twisting and distortion of leaves, and ring patterns on fruit. Some peaches show breaks in coloration on flower petals. Apricots become lumpy and small with bitter flavor. Garden plums develop strong yellowy mosaic patterns on the leaves, sunken ring patterns called “pox” in the fruit, and drop their fruit prematurely.

In 1992, plumpox jumped to the Western Hemisphere, showing up in Chile. In 1999, it appeared in the U.S., in southern Pennsylvania followed by Canada in 2000. All infected orchards and homeowner trees in those areas have been removed. Federal officials implemented strict quarantine measures immediately after the disease was identified, and destroyed orchards and garden trees in fruit-producing areas known to have the disease. Surveys are continuing with the hope of total eradication of plum pox from the United States.

Note: Dr. Vernon Damsteegt, Research Plant Pathologist USDA-ARS, FDWSRU provided the information in this news release.

For more information about plum pox and other Invasive Species of Concern, visit www.mdinvasivesp.org or call MDA at 410.841.5920.

photos available electronically on request